This invention relates to a color image forming method. More particularly, it pertains to a color image forming method having a rapid silver bleach-fixing ability.
Generally speaking, for obtaining a color image by processing of a light-sensitive silver halide color photographic material subjected to imagewise exposure, there is provided the step of processing the metal silver formed with a processing solution having bleaching ability after the step of color developing step.
As the processing solution having bleaching ability, there have been known bleaching solutions and bleach-fixing solutions. When a bleaching solution is employed, the step of fixing silver halide with a fixing agent is usually added subsequent to the bleaching step, but in some cases the bleach-fixing processing performing bleaching and fixing in one step may be practiced.
In the processing solution having bleaching ability in processing of color light-sensitive materials, inorganic oxidizing agents such as red prussiate, dichromate, etc. have been widely used as the oxidizing agent.
However, the processing solution having bleaching ability containing these inorganic oxidizing agents has been pointed out to involve some serious drawbacks. For example, red prussiate and dichromate are relatively excellent in bleaching power of the image silver, but they have properties undesirable in prevention of pollution, because there is the fear that cyan ions or hexavalent chromium ions harmful to human bodies may be formed by decomposition with light. Also, these oxidizing agents have very potent oxidizing power and they can hardly be permitted to co-exist with a silver halide solubilizing agent (fixing agent) such as thiosulfate, etc. in the same processing solution, and it is almost impossible to use these oxidizing agents in the bleach-fixing solution, thus making it difficult to accomplish the object of rapid and simple processing. Further, the processing solution containing these inorganic oxidizing agents has the drawback that it is difficult to regenerate it for reuse without discarding the waste solution after processing.
In contrast, as a processing solution causing little problem of pollution and suited for the requirement of more rapid and simplified processing as well as possiblity of regenerated use of the waste solution, a processing solution utilizing a metal complex of an organic acid such as aminopolycarboxylic acid metal complex, etc. is coming into use. However, the processing solution employing a metal complex of organic acid, due to its weak oxidative power, has the drawback of slow bleaching speed (oxidation speed) of the image silver (metal silver) formed in the developing step. For example, iron (III) ethylenediaminetetraacetate complex, considered to have a potent bleaching power among aminopolycarboxylic metal complexes, has been practically applied as the bleaching solution and the bleach-fixing solution in some uses, but in high sensitivity color light-sensitive materials comprising mainly silver bromide, silver iodobromide emulsion, particularly color negative film, color reversal film for photography containing silver iodide as the silver halide, it is insufficient in bleaching power and traces of image silver will remain even after prolonged processing, resulting in bad desilverization. This tendency will be more marked in a bleach-fixing solution where thiosulfate and sulfite co-exist, because the redox potential is lowered. Particularly, it has been found that the desilverization characteristic is markedly bad in a high sensitivity color light-sensitive material containing silver iodide for photography containing black colloid silver for halation prevention.
Further, as a silver halide emulsion, which is a high sensitivity emulsion containing silver iodide, micropulverized and suited for the requirement of resource protection with effective utilization of silver, there is the core-shell emulsion has been recently developed. The core-shell emulsion is a mono-dispersed core-shell emulsion which is prepared by utilizing the preceding silver halide emulsion as the crystal nuclei, then laminating successively the subsequent precipitate, while controlling intentionally the composition or the environment with lapse of time for respective precipitates. Among them, the aforesaid core-shell type high sensitivity emulsion containing silver iodide in the core and/or the shell has an extremely preferable specific feature in photographic performance, but when applied in a conventional bleach-fixing bath for a color light-sensitive material, it proved to be very poor in bleach-fixing characteristic of developed silver and silver halide.
For example, the developed silver in the silver halide emulsion for photography containing 0.5 mole % or more of silver iodide, particularly the developed silver of the silver halide containing 0.5 mole % or more of silver iodide in the core and/or the shell in the core-shell type emulsion, although being excellent in sensitivity, graininess, covering power, etc., is markedly bad in bleaching characteristic in the color light-sensitive material in which the developed silver must be bleached, due to the form of the developed silver which is different from that of the prior art.
Alternatively, attempts have also been made of utilizing flat plate silver halide grains as disclosed in Japanese Provisional Patent Publications No. 113930/1983, No. 113934/1983, No. 127921/1983 and No. 108532/1983. Even if the photoquantum number captured by silver halide grains may be increased by use of the flat plate silver halide grains, the amount of silver employed is not increased and there occurs no worsening to image quality, as discussed in these specifications. However, even with the use of such flat plate silver halide grains, the developed silver formed by development with a p-phenylenediamine type color developing agent has the drawback of poor silver bleaching characteristic. Accordingly, it has particularly strongly been desired to have a processing solution which is capable of bleach-fixing rapidly a color light-sensitive material comprising a core-shell emulsion and/or flat plate silver halide emulsion containing silver iodide having excellent features as described above and also having a halation preventive layer comprising black colloid silver.